This invention relates to foundation units, often known as box springs, and more particularly to a spring element for a foundation unit, and the resulting foundation unit, the spring element being composed of a bent wire member with torsion segments rather than a coventional coil spring.
Foundation units of the type of the present invention are typically composed of coil springs mounted on a wooden frame which are reinforced and held in place by a grid wire top bearing structure. Coils are secured to the grid wire top bearing structure by a series of clips, pigtail wires or the like, or, as described in U.S. Pat. No. 3,953,903, assigned to the assignee of the present application, the coil springs may be snapped into a specially formed grid wire top bearing structure. However, the foundation unit of U.S. Pat. No. 3,953,903 employs conventional coil springs, which, although quite satisfactory for many applications, tend not to provide desired support under all load conditions. Therefore, other types of wire elements, such as those illustrated in U.S. Pat. Nos. 4,377,279 and 4,770,397, have been developed, the elements having a full range of characteristics from no spring whatsoever to coil spring-like characteristics.